1. Field of the Invention
The present invention relates to magnetic markers applied to articles,, for identifying the kind, quantity and the like of the articles, and also relates to a reading and identifying apparatus therefor.
2. Description of the Prior Art
It has been known to apply markers to articles so as to count the number of the articles or to use the markers for burglar-proof measures by reading the markers. Further, it has been desired that such markers are small and cheap. Since these markers are attached to articles in such a way that they are not directly visible in order to prevent the markers from being intentionally or carelessly damaged, magnetism, microwaves and the like have been used for reading the markers. For example, amorphous magnetic thin, strips or fine wires which are read with the aid of magnetic fields, aluminum films which are irradiated with microwaves and the like have been used for the markers. In one particular, system, amorphous magnetic material markers which are applied to the articles to be detected are allowed to pass through an a.c. magnetic field in order to detect variations in the magnetic flux which occur in the amorphous magnetic materials. This system effectively utilizes the soft magnetization characteristics of the amorphous magnetic materials, and has the following desirable features: The markers are not subjected to serious, restrictions on the positions where the markers are attached or the kinds of articles to be detected, and the makers are highly sensitive and can be small and light in weight.
The main portion of a conventional magnetic marker reading and identifying apparatus is schematically shown in FIG. 1. In this figure, a magnetic marker 1 made of amorphous thin strips or fine wires is applied to an article 2 which is set on a belt 4 stretched between two pulleys 3, and is moved in a direction indicated by the arrow as the belt 4 runs. FIGS. 2(A) and 2(B), which are enlarged views, shown an exciting coil 5, an a.c. oscillator 6, detecting coils 7 and a measuring instrument 8. The exciting coil 5 for generating an a.c. magnetic field is connected to the a.c. oscillator 6 The detecting coils 7 detect, as an induced voltage, variations in the magnetic flux in association with a reversal of magnetization of the magnetic marker 1. The detecting coils 7 are connected to the measuring instrument 8, which identifies a voltage pulse train produced in the detecting coils 7 by means of, pattern recognition. Twin coils are used for the detecting coils 7 in order to cancel out induced voltage produced in the detecting coils 7.
The magnetic marker is composed of a plurality of magnetic thin strips or fine wires which are made of a Co base amorphous alloy or the like. However, a magnetic marker 1 which is fixed on a plastic element can be used for the same purpose.
In this apparatus, when a plurality of articles 2, i.e. objects to be detected, on which the magnetic markers 1 are applied pass over the exciting coil 5, being conveyed by the belt 4 as shown in FIG. 1, voltage pulses produced in the detecting coils 7 according to the a.c. magnetic field generated by the exciting coil 5 are detected, and the kinds of the articles are identified by the measuring instrument 8.
The above-mentioned magnetic marker made of amorphous magnetic materials is usable, but still offers the following problems which should be solved:
First, the identifying ability of the marker is a matter of concern. Conventionally, such markers are composed of fine strips or thin wires which are made of materials having one and the same magnetic characteristics. Therefore only data as to whether the marker or the article is present or not and as to the number of articles can be obtained by measuring voltage pulse produced by the magnetic field, but sorted articles cannot be identified. It would be desirable, for example, to use such markers for sorting and counting several identical products for each manufacturer. Accordingly, it would be advantageous to improve the arrangement and the manner of use of markers.
Second, a rapid variation of the magnetic flux is preferable, when the variation in the magnetic flux which is, generated in the amorphous magnetic substance due to the a.c. magnetic field is detected as an induced voltage by the detecting coils, because a steep voltage pulse can that be obtained in the detecting coils. A steep voltage pulse would make the detection of the voltage pulse easy and would substantially avoid effects by magnetic field disturbance. In order to produce a rapid variation in the magnetic flux, it is necessary to use a magnetic material which has .PHI.(magnetic flux) - H(magnetic field) magnetic hysteresis characteristic showing a square hysteresis loop. The shape of the magnetic material must be determined so as to decrease the demagnetizing field in order to maintain the square hysteresis loop characteristic. That is, the shape of the marker should be selected so that its length is sufficiently large in comparison with the width thereof. As a result, the size of the marker becomes larger as a whole.
Further, the installation condition of the exciting coil 5 causes a problem in the conventional magnetic marker reading and identifying apparatus shown in FIG. 1. That is, only one exciting coil is disposed below the belt 4 on which articles 2 are set. Since the positions and directions of the articles on which the magnetic markers 1 are applied are not always uniform on the belt 4, the outputs which are delivered from the detecting coils 7, when the magnetic markers 1 passes through the a.c. magnetic field area effected by the exciting coil 5, vary in response to the positions and directions of the articles on the belt so as to be unstable.